Although obstructive sleep apnea affects 2-4% of the middle-aged population and is a major public health problem the pathogenesis of this disorder is unknown. The focus of this research is to understand the mechanisms leading to sleep apnea by evaluating the structure and function of the upper airway using magnetic resonance imaging techniques during wakefulness and sleep. MRI techniques uniquely afford the ability to directly visualize, quantify, and link parameters relating to the anatomy, tissue composition, and dynamic biomechanical properties of the pharyngeal soft tissues. The investigators have studied the biomechanical role of upper airway soft tissue structures in mediating collapse of the airway with novel magnetic resonance tagging techniques.